Method of oxidizing aromatic side-chain compounds



March 16 1926. 1,576,999

P. SEYDEL METHOD OF OXIDIZING AROMATIC SIDE CHAIN COMPOUNDS Filed July le. 1921 Charge l T/PePmOWeZ'e?" Oxygen or 9a@ N672 n @luz/gen acm? y 4 Toluene I May/gamas? dzozzde A TTURNE Y Patented Mar.4 16, 1926.

.UNITED STATES PATENT oFF-ler..

PAUL SEYDEL, F JERSEY CITY,

NW JERSEY, ASSIGNOR, BY MESE ASSIGNMENTS,

T0 BEYDEL CHEMICAL COMPANY, OF NEW' YORK, N. Y., A CORPORATION OF WEST M-ETHOD 0F DXIDZING AROMATIC SIDE-CHAIN COMPOUNDS.

Application led July 16, 1921.

To all whom it may cmern: Be it known that l, PAUL SEXUEL, a citizen of the United States, residing at Jersey hereby declare the vfollowing to he a fullv 9 clear, and exact description of the invenl@ tion, such as Will enable others skilled in the art to `which it appertains to malte and use the same.

` 'lihis invention relates to the oxidation of aromatic organic compounds containing an oxidizable side-chain, and has for its'object the production, lin an economical and commercially feasible manner, of an varomatic acid ot' a high degree of purity and more particularly of beni/Loic acid suitable for use as a food preservative or for the production of various pharmaceutical and medicinal preparations. r

Heretoitore in converting aromatic sidechain compounds into their corresponding acids, methods involving the use of various oxidizing;r -agents such as sul'uric-chromic acid. mixture, permanganate, persultate, nitric acid (in conjunction with chlorine), and manganese dioxide (with sulfuric acid) have commonly heen employed. @t these methods the three Erst mentioned involve the use of expensive chemicals which can not he readily or economically recovered and they are, therefore, entirely un suited for the economicalproduction of an aromatic acid on a commercial scale.

rllhe two remaining methods, While not open to this particular objection as to cost of reagents, each possesses, nevertheless, certain other disadvantages which render its use inconvenient and expensive, especially Where purity of product is an important requirement, as in the present case. Thus the manganese dioxide-sulfuric acid process, when applied to the production of benzoic acid from toluene, yields a crude product containing tarry impurities which are exceedingly difhcult to remove from the aromatic acid and for this reason the cost of production of a highly purified product is excessively high. The formation of tarry products is due to the diiliculty of controlling the oxidation so as to prevent the oxdation from proceeding too far, resulting in Serial No. 485,342.

the formation of oxidation products other -than the aromatic acid. Even the formation of a considerable amount of carbon dioxide is not readily avoided when this method is empio ed.

(ln the other and, while it is true that the course of the oxidation can be better regulated and controlled hy means ot the chlorine-nitric acid method of oxidation so that the production of tarry impurities and other oxidation by-products is largely avoided, yet this'method involves another diiiiculty which renders its use altogether objection- I able for the production of benzoic acid of a high degree of purity. This difliculty arises from the fact that certain chlorine substitution products in which the chlorine is in the `oenzene nucleus are formed during the course of the reaction and these are exceedingly diihcult to'remove from the henzoic acid. These chlorine substitution products are particularly objectionable as impurities in the henzoic acid Where the product is to he used as a preservative or for certain pharmaceutical purposes, and in these instances, even theuslghtest traces of these chlorinated impurities must he altogether avoided.

The process of the present invention avoids all the foregoing diiiiculties and in addition may becarried out in a highly economical manner and practically Without loss of any of the raw material. Furthermore the oxidation hy means of this process can he carried out in an especially short period of time thereby economizing in laborand equipment and resulting in an unusually low cost of production in comparison with any of the older methods.

' The method of the present invention depends u on. the direct oxidation of the aromatic side-chain compound by means of nitric acid under specially controlled conm ditions, particularly with respect to the pressure under which the oxidation is carried out. Another important feature of the present invention is the use of an accelerator or catalyst inrconnection with the nitric acid. Other novel features of the process lie in the inter-relation or inter-action of the nitric acid and the auxiliary oxidizing agent 'or catalyst and also in the proper regulation and mutual adjustment of the temperature and pressure, under which conditions the active oxidation of the aromatic com ound takes place. Still another feature of t e invention is the regulation and control of the concentration of the gaseous oxides of nitrogen in or above the reaction mixture during the course of the oxidation.

This regulation and control of the concentration of the gaseous oxides of nitrogen is brought about in part by introducing at intervals into the reaction chamber the proper amount of concentrated gaseous oxygen and also by the removal from the reaction chamber at certain intervals of the spent or exhausted oxides of nitrogen (mainly lower oxides) formed during the reaction. By these means the speed and course of the oxidation can be controlled and regulated in such manner that practically the whole of the aromatic side-chain compound is converted into useful products, principally the aromatic acid, and at the same time the complete oxidation can be carried -out in a remarkably short period of time and substantially without loss of nitric acid or aromatic compound.

One of the most remarkable features of the new recess is the effect of the above mentioned) control of thel concentration of the oxides of nitrogen and of the pressure upon the speed of the reaction. This is strikingly illustrated by the fact that at a given temperature the reaction may be completed in a shorter time by employing these means than is required for completing the reaction a't even an appreciably higher temperature when the above mentioned regulation of pressure and concentration of gas is lnot em loyed. This is in addition to a greatly lncreased yield.

The process of the present invention may be carried out in Various types of apparatus, but I have found the new apparatus described in the following paragraphs to be especially well adapted for carrying out my new process. The various novel features of both the process and the apparatus and the advantages gained thereby will appear more clearly from the following detailed description of the apparatus and the manner of using the same for carrying out my new improved process.

The apparatus in its preferred form is made of a' corrosion-resisting metal, preferably an iron-silicon alloy containing a high percentage of silicon, such as the alloy known as duriron or tantiron and comprises a 500 gallon kettle, 1, provided with a steam jacket, 2, for heating the same, and provided also with an opening 3 in the top for introducing the charge into the kettle. The cover 4 is provided with clamps and a asket by means of which the opening 3 may e ti htly closed so as to prevent the escape of t e asese under pressure within the kettle. he cover 4 is further provided with a window 5 for viewing the chan es in the appearance of the materials whic take place during the progress of the reaction. The kettle` is provided further at the upper part thereof with an opening 6 leading into the exit pipe 7 and the pressure safety valve 8 by means of which a portion of the gaseous mixture is allowed to escape from the kettle to reduce the pressure therein. The pipes 28 and valve 29 are connected with a suitable acid-recovery equipment 30 illustrated diagrammatically, such as an acid tower or a seriesvof Woulfe bottle of the type and arrangement commonly used Vfor concentrating or recovery of nitric acid. An inlet tube 9 and valve 10 connecting with the tubes 2G and 27 serve as a means for introducing compressed oxygen or other gas rich in oxygen under pressure into the reaction mixture in the kettleat certain stages of the reaction. The thermo-couple or resistance element 11 extends into and is surrounded by the thermometer well 12 fitted into the top of the kettle and is connected with the recording element 13, which records the approximate temperature of the mixture throughout the course of the reaction. A recording pressure-gauge 14 is connected through the U tube 15, containing oil and the tubes 26 and 27 to the upper portion of the kettle through the opening 16. The steam jacket is connected through the inlet tube 17 and the valve 18 with a steam boiler or other source of steam, The pressuregauge 19 is connected through the tube 2U to the steam jacket. The steam jacket is further provided with an outlet tube 21 and valve 22. The kettle is further provided at the bottom with a wide opening 23 leading into the short wide pipe 24 which extends through the outer wall of the steam jacket and is provided with a valve 25.

In carying out a typical example or ernbodiment of the process of my invention, the kettle is charged through the opening 3 with 850 pounds of 67 per cent nitric acid, 800 pounds of water, 500 pounds of toluene and 5 pounds of manganese dioxide. The concentration of the nitric acid in this typical charge is 35 per cent. The total weight of 100 per cent HNO8 is 570 pounds and the charge contains one pound of toluene to each 1116 pounds of 100 per cent nitric acid.

After the charge has been introduced into the kettle, the cover 4 is clamped in place and the temperature is brought by means of the steam in the steam-jacket gradually to 80 to 900 C., at which Vtime the pressure in the kettle will usually be about 35 to 40 pounds er square inch. The period of this gra ual rise of temperature is about two hours. After the temperature and pressure have reached the last mentioned values, they are maintained at about this range of magnitude for a period of from about six the active or oxidizing oxide of nitrogen at a more or less constant concentration and also to lower the pressure. This 1s accomplished by opening the release valve 29A which connects the exit pipe 28 with the recovery apparatus, 30, illustrated. diagrammatically in the drawing, tor recovering spent oxides of nitrogen, toluol-vapor, etc. This release of spent gases and subsequent introduction of oxy en under pressure is preierably repeated t ree or tour times during the 94 hours required for completion of the operation, the pressure being eventually raised to about 7,521 pounds and the temperature to about the ooiling point of toluene or about C.

At the lend of 2dhours the reaction is completed and the reaction mass contains an amount of benzoic acid corresponding to a yield of 'from 70 to 80 per cent of the theoretical. This reaction mass, when hot, is in a liquid state. lt may be poured or dumped into a tank suitable for this purpose. @n cooling lthe mass will form a solid cake.

rlhis cake is freed from the spent nitric acid and is purified by tirst neutralizing the crude benzoic acid with caustic soda or soda ash, precipitating benzoic acid from this salt with. a strong mineral acid, washed using preferably a continuous acid prooi filter, such as a filter of the type known as the Qliver lter. rlhe lter cake of benzoic acid is centrifuged in order to eliminate the greater portion of the moisture and is then dried and finally sublimed to obtain the pure finished product,l

lt will be understood that the foregoing example of the process ot my invention is given by way oi' illustration and l do notr restrict my linvention to the details described therein, but l may vary the conditions and the procedure-without departing from my invention in accordance with the description of the main features of my invention given above.

rlhus, l may vary the quantity and the strength oi' the nitric acid used per pound ot' toluene and ll may also vary the quantity of manganese dioxide or l may use other nitric oxide catalysts, such as vanadium oxide and the like. Also l may vary the pressure between 35 pounds per squarel inch and 804 pounds per square inch or higher and I may also begin the reaction with less .water than that specified and employ such an amount of nitric acid as will give the required strength (approximately 30 to 40 per cent) and as the oxidation roceeds and the strength of the acid wea rens, I may add a fresh quantity of strong n itric acid from time to time during the course of the reaction, thereby maintaining approximately the same strength of nitric acid during the entire period ot' oxidation.

Also instead of carrying on the'operation continuously, say for 24 hours, the opera tion may be interrupted, in order to make either two periods or shiftsmof 12 hours or three periods of 8 `hours or several eriods of still shorter duration, thus facilitating the addition of i'resh materials at-the close of these diderent operating periods,

when the apparatus and 'reaction mixture have cooled somewhat. ln this manner the concentration of the nitric acid and the relative proportion of manganese dioxide, the relative proportion of Waterand of toluene can be held at approximately constant values and the reaction controlled to better advantage by any or all of these means.

rlhe object of introducing oxygen under pressure into the apparatus' is to oxidize the lower and inactive oxides of nitrogen into the higher and active oxides oi: nit-ro- ,qen and in this manner to aid in maintaining the concentration of the active oxides ot nitrogen at a more nearly constant and favorable value, the venting of the spent oxides of nitrogen and other inactive gases contributing also to this same end.

rlhe manganese dioxide, which is added at intervals in small portions so as to have at the end of the experiment about l0 pounds to each 500 pounds of toluene, hastens the oxidation, l believe, by its catalytic action on the nitric acid or probably by reaction with the latter to form an intermediate product which is later decomposed by reaction with the toluene.

After the completion of the operation, whatever slight amount of benzoic acid which is not dissolved in the hot weak nitric acid is contained in the oily layer composed of the unreacted toluene and some oily luy-products of the reaction, mostly various nitro-toluenes, condensation products, ketones, etc., but no considerable amount of benzaldehyde. After cooling the reaction. produit and separating the crude benzoic acid, the unreacted toluene and nitric acid are utilized vfor making up the next charge for the reaction kettle. Also the nitric acid and toluene recovered from the vented gases by means of the recovery apparatus are utilized in the same manner.

The proportion of nitro products formed and separated with the crude benzoic-acid is usually about 5 to ,10 per cent. However, these nitro products are valuable and can be recovered. This is done by exercising special care inv subliming the benzoic acid' so as not to exceed a certain temperature which leaves behind the nitro-benzoic acid which maybe separated through fractional crystallization of their salts or by ain other convenient method. The amount o nitroproducts formed var according to the strength of the nitric acid used, being greater if the strength of the nitric acid is increased. Thus, it will be seen that from 90 to 95 per cent or more ofthe toluene is converted entirely into valuable and marketable commercial products, benzoic acid constituting from to -80 per cent of the yield and the nitro-benzoic acidV and the few other by-produrts constituting the remaindcr.

In purifying the crude benzoic acid the latter is treated with an alkali, referabl sodium, although calcium and ot eri/neta lic oxides or carbonates will serve. It is best treated either With caustic soda or sodiumv carbonate, which brings it into solution and makes easy the se aration in conical tanks (or other tanks esigned to separate two layers of liquids) from the oily substance, mainly toluol, nitro toluol, etc. This solution, when evaporated, will give a technical sodium benzoate.. In order to obtain a C. P. roduct, it is advisable to precipitate the acid from its salt solution; thoroughly Wash it in centrifugal machines or suction filters, provided with Washing devices, dry the cakes obtained and either crystallize the acid from hot Water, or preferably sublime it at a temperature sufficiently low to prevent carrying over the nitro acids present.

The oxidation of the nitro-toluenes into their corresponding iiitro-benzoic acids proceeds in very much the same manner as the oxidation of the toluene itself; the action being more active and indeed under some circumstances being even violent, I take good care to closely observe temperatures, pressures and the relativity of the gaseous and liquid oxidizers to the amount of nitrotoluenes present.

I claim:

1. The method of oxidizing an aromatic side-chain compound which comprises subjecting it to the action of nitric acid under a pressure of from about 40 to 80 pounds per square inch, substantially as described.

2. The method of oxidizing an aromatic side-chain compound which comprises subjecting it to the action of nitric acid of a concentration of about thirty to forty per cent under a pressure or from about 40 to pounds per square inch, substantially as described.

3; The method of oxidizing an aromatic sdie-chain compound which comprises subjecting it to the action of nitric acid under pressure and maintaining the concentration of the nitric acid at a relatively constant concentration throughout the main part of the oxidation process, substantially as described.

4. In the method of claim 2, maintaining the concentration of the nitric acid at a relatively constant concentration throughout the main part of the oxidation process and under a pressure of from about 40 to 80 pounds per s'uare inch, substantiall as. described.

5 he method of oxidizing toluene to benzoie acid which comprises subjecting the .toluene to the action of nitric acid of about thirty to forty per cent concentration at a temperature of from about 70 centigrade to 110 centigrade and under a pressure of from about 40 to 80 pounds per square inch, substantially as described.

6. The method of oxidizing an aromatic side-chain compound which comprises subjecting it to the action of nitric acid under pressure in the presence of a catalyst containing loosely combined oxygen, substantially as described.

7. The method of oxidizing an aromatic side-chain compound which comprises subjecting it to the action of nitric acid under a pressure of from about 40 to 80 pounds per square inch, in the presence of a catalyst containing loosely combined oxygen, substantially as described.

8. The method of oxidizing an aromatic side-chain compound which comprises subjecting it to t a concentration of about forty per cent under pressure in the presence of a metallic oxide catal st, substantially as described.

9. ln the method of oxidizing an aromatic side-chain com ound which comprises subjecting it to t e action of nitric acid of a concentration of about forty per cent under pressure maintaining the concentration of the nitric acid ata relatively constant concentration throughout the main part of the oxidation rocess in the presence of a catalyst containing loosely combined oxygen, substantially as described.

10. The method of oxidizing toluene to benzoic acid which comprises subjecting the toluene to the action of nitric acid under ressure and at a temperature of from about 0 lcentigrade to 110o centigrade in the presence of a catalyst containing loosely combined oxygen, substantially as described.

11. The method of oxidizing toluene to benzoic acid which comprises subjecting the toluene to the action of nitric acid of about forty per cent concentration and at a temperature of from about 70 centigrade to 110 centigrade under pressure in the presence of a catalyst containing loosely combined oxygen, substantially as described.

l2. The method of oxidizing toluene to benzoic acid which comprises subjecting the toluene to the action of nitric acid of about e action of nitric acid of forty per cent concentration and at a temperature of from about 70 centigrade to 110 centigrade under a pressure of from about 40 to 80 pounds per square inch in the presence of a catalyst containing oxygen,

'substantially as described.

13. The method of oxidizing an aromatic side-chain compound which comprises subjecting it to the action of nitric-acid under pressure in the presence of an oxide of manganese, substantially as described.

14. The method of oxidizing an aromatic side-chain compound whichcomprises subjecting it to the action of nitric acid under a pressure of from about 40 to 80 pounds per square inch in the resence of an oxide of manganese, substant1ally as described.

15. The method of oxidizing an aromatic side-chain compound which comprises subjecting it to the action of nitric acid of a concentration of about forty er cent under pressure s in the presence o an oxide of manganese, substantially as described. 4

16. The method of oxidizing toluene to benzoic acid which comprises subjecting the toluene to the action of nitric acid of a concentration of about forty per cent under a pressure of from 40 to 80 -pounds per square inch in the presence of an oxide of manganese, substantially as described.

17 In the method of oxidizing toluene to benzoic acid which comprises subjecting the toluene to the action of nitric acid of a concentration of about forty per cent, maintaining the concentration of the nitric acid at a relatively constant concentration throughout the main part of the oxidation process in the presence of an oxide of manganese, substantially as described.

18. In the method of oxidizing toluene to benzoic acid vwhich comprises subjecting the toluene to the action of nitric acid` of a concentration of about forty per cent, maintaining the concentration of the nitric acid at a relatively constant concentration throughout the main part of the oxidation process and under a pressure of from about 40 to 80 pounds per square inch in the presence of an oxide of manganese, substantially as described.

19. The method of oxidizing toluene to benzoic acid which comprises subjecting the toluene to the action of nitric acid under pressure at a temperature of from about 70 centigrade to 110 centigrade in the presence of an oxide of manganese, substantially as described.

20. The method of oxidizing toluene to benzoic acid which comprises subjectin the toluene to the action of nitric acid of a out forty per cent concentration and at a temperature of from about 70 centrigade to -tion catalyst, substantial?7 21. The method of oxidizing toluene to benzoic acid which comprises subjecting the toluene to the action of nitric acid of about forty per cent concentration and at aj temperature of from about centigrade to 110 centigrade under a pressure of from about 40 to 8O pounds per square inch in the presence of an oxide of manganese, substantially as described.

' 22. The method of oxidizing an aromatic side-chain compound which comprises subjecting it to the action of nitric acid under pressure, carrying out the oxidation in an atmosphere containing oxidizing oxides of nitrogen, maintaining the concentration of the oxidizing gaseous oxides of nitrogen at a relatively constant value by introducing substantially pure oxygen under pressure into said atmos here and removing non-oxidizing gases rom said atmosphere, substantially as described.

23. In thev method of claim 6, maintaining the ratio of the weights of nitric acid to catal st at a relatively constant value, substant1ally as described.

24. The method of oxidizing an aromatic side-chain compound which comprises subjecting. it to the action of nitric acid under a pressure of from about 40 to 80 pounds per'square inch in the presence of an oxidaas described.

25. The method of oxi izing an aromatic side-chain complound which comprises subjecting it to t e action of nitrlc `acid of about thirty to forty percent concentration under a pressure of from about 40 to 80 pounds per square inch in the presence of an oxidation catalyst, substantially as described.

26. The method of oxidizing toluene to benzoic acid which comprises subjecting the toluene to the action of nitric acid under a pressure of from about 40 to 80 pounds er square inch and at a temperature of rom about 70 centigrade to 110 centigrade in the presence of an oxidation catalyst, substantially as described.

27. The method of oxidizing toluene to benzoic acid which comprises subjecting the toluene to the action of nitric acid of about thirty to forty per cent concentration and at a temperature of from about 70 centigrade to 110 centigrade under a pressure of from about 40 to 80 pounds per square inch in the presence of an oxidation catalyst, substantially as described.

In testimony whereof I ailix my signature.

PAUL SEYDEL. 

